Coronary artery bypass grafting (CABG) with autologous human saphenous vein (HSV) is the best available treatment for severe coronary heart disease, but long-term graft patency is problematic. The per patient vein graft failure 12-18 months after CABG was 45% in the recent PREVENT IV trial (N=1,920). Vein graft failure predisposes patients to additional operations, myocardial infarction, recurrent angina, limb loss, and death. Graft failure is primarily attributable to intimal hyperplasia (IH), the process by whic vascular smooth muscle cells (VSMCs) migrate, proliferate, and deposit extracellular matrix (ECM) into a neointima that causes stenosis. We have identified MAPKAP kinase II (MK2) as a potential target for pharmacological intervention for preventing vascular graft IH. MK2 is activated directly by p38 mitogen activated kinase (MAPK), which is triggered by the mechanical and environmental stresses on the graft during transplant. Because p38 MAPK functions are diverse, p38 inhibitors cause undesirable side effects. Thus, MK2 is a logical target for inhibitin a proximal trigger of IH, and the central hypothesis of this proposal is that sustained intracellulr pharmacological inhibition of MK2 will prevent IH and improve long-term graft patency. A cell- penetrating peptidic MK2 inhibitor (MK2i) developed by project collaborators has high specificity and low toxicity, but barriers against intracellular delivery hinder its efficacy. Mechanistic studies support the notion that MK2i has promising anti-inflammatory and anti-fibrotic activity, but its potency and longevity of action are limited by internalization into and sequestration within intracellular late endosomal vesicles. To overcome the endosomal barrier, a novel polymer-based MK2i nanoplex (MK2i-NP) design has been developed in the PI's lab that improves cell internalization and endosomal escape of the MK2i peptide. Our published data verify that formulation of MK2i into endosomolytic MK2i-NPs increases peptide intracellular delivery and produces more potent and longer-lasting bioactivity relative to treatment with the free peptide. Rapid uptake and durable intracellular retention of MK2i-NPs are key criteria for this application because a brief (30 minute) treatment of the HSV tissue at the time of explant, during the period when the surgeon is preparing the site where the anastomosis will be placed, must protect the graft throughout the post-surgery healing phase. This project seeks to optimize and better elucidate the mechanism of MK2i-NPs and then to test this therapy for efficacy in inhibiting IH pathogenesis in advanced preclinical models.